Pneumatic mandrels and chucks, the latter including shaftless and core-bar mounted chucks, have come into prominent use in the roll handling field within the past twenty years. Typically these mandrels are inserted into the cores of roll stock, e.g. a paper, plastic, woven or non-woven web of material, and expanded to grip the inner surface of the cores by application of compressed air to a neoprene or rubber bladder internal of the mandrel. The elastic bladder expands against leaves, lugs or buttons which move radially outward to grip the inner surface of the core, or the web stock itself when no core is used. A good orientation into the types of expandable air shafts can be found in "The ABCs of Expandable Air Shafts" by Stephen H. Albee, Graphic Arts Monthly, April 1977, pp 52-56. The October 1975 issue of Paper, Film & Foil Converter on pp 52, 66, and 93 describes generally the products of Nim-Cor, Inc., Tidland Corp., and Double E Company, Inc., all manufacturers of various types of air shafts.
There are five basic types of air shafts: Leaf (movable, one fixed, and trapper leaf); Large Button; Small Button; Lug; and C-shaped dual Fiberglass Sleeve type. There are numerous specialty styles including slitter knife and square shaft types. As stated in the Albee article, p 52: "Whatever the style, all air shafts share one basic principle. A metal tubular body acts as the load-carrying member. This shaft contains a number of drilled holes or slots into which are fitted metal buttons or lugs backed with steel pressure flanges. When air is injected into the shaft, an internal air bladder expands, forcing the buttons or lugs radially outward until they securely grip the inside diameter of the roll core along its full length.
"The internal air bladder, made of tear-resistant neoprene or similar material, has bonded ends or metal fittings that form an airtight flexible chamber. Air pressure of approximately 80 lbs. per sq. in. is necessary to ensure that the outward thrust of the buttons is sufficient to grip the core properly.
"When the air is released, the bladder deflates, causing the spring-loaded buttons or lugs to retract below the outside surface of the shaft. This allows quick and easy removal of the shaft from the roll."
Atlo Tool and Engineering offers an "Equalizer" brand air shaft having four conventional outer leaves mounted on pusher pins extending through the tubular main body of the shaft. An inner rubber tube (bladder) exerts pressure on inner leaves which are connected to the outer leaves by pusher pins. This construction is claimed to prevent eccentric chucking due to a spring between the pusher pin and inner leaf, and the limited travel of the inner leaf which is due to special marginal edges which contact the inner surface of the main body. The Western Tool and Manufacturing Co., Inc. provides a Patton AeroShaft having a single longitudinal fluted rib which expands to grip the core.
The leaf, button and lug type air shafts are all relatively complex, requiring many internal, linked, moving parts with spring return, pusher pins, screw connections and the like. The rubber bladder deteriorates with age and is subject to blow-outs. Further, since it will preferentially expand where it is not confined, rubber bellows tend to cause the shafts to grip the roll cores off center axis. This is because those leaves, lugs, buttons or sleeves that touch the core first in one area tend to offer greater resistance to bladder expansion as compared to other expanding leaves, which expand till they meet equal resistance. Since the shaft is typically inserted in roll cores off axis to start, true centering and rotational balance is often not achieved.
As the rolls turn, they start to work up and down on the shaft, gradually becoming loose. Vibration and pulsation cause variation in web tension. In turn, this causes loss of product quality and, quite often, breakage of the web stock. The complex leaf mechanisms can get jammed during shaft flexing, the springs break, and the internals can collect paper dust and waste. In addition to high initial cost, the maintenance downtime and cost can be considerable. To this must be added the cost of slippages, stock jamming in presses, loss of tension control and waste left on the rolls.
The fiberglass sleeved shafts are basically a variation of the leaf type in which two generally C-shaped fiberglass sleeves are used in lieu of leaves and in conjunction with a high tensile aluminum shaft body. The fiberglass outer sleeve has a zig-zag gap which opens to accommodate the expansion of the rubber inflating element and smooth-surfaced inner sleeve. This type of shaft is used primarily only where low handling weight is of prime importance.
Accordingly there is a need for a simple, pneumatic air shaft that provides full grip along its length, has a high strength to weight ratio, is able to handle the high speed and heavy load conditions of today's web processing equipment, offers true centering for rotational balance, non-eccentric rotation, and even tension control, is relatively low cost, and is easy, simple and faster to maintain.